The present invention relates generally to manufacture of optical devices. More particularly, the present invention provides a laser device and method using a preferred cleave orientation, which facilitates parallel facets and reduced surface roughness. Although the invention has been described in terms of cleaving, it would be recognized that other ways of forming the facet can be used. As an example, the facets can be etched, cut, separated, split, among others. Additionally, the invention can also be applied to other forms of devices such as light emitting diodes, integrated circuits, MEMS, medical devices, combination of these, among others.
Human beings have been attempting to develop new types of solid materials from the early days. From the stone-age to the electronic age, human beings have progressed through stone, brass and copper, steel, plastics, and now semiconductors. An example of a commonly used semiconductor is silicon. Silicon is used extensively in the manufacture of integrated circuits, which form the basis of electronic devices and systems, including cellular phones, computers, video games, and solar panels. Other types of semiconductor materials have also been proposed.
One such semiconductor material that has gained popularity is gallium nitride, commonly called “GaN.” GaN serves as the basis of blue colored light emitting diodes, which were pioneered by a famous inventor named Shuji Nakamura. Most recently, considerable progress has been made in recent years in the fabrication of gallium nitride based laser diodes, which are useful for optical data storage, such as Blu-ray™ digital video discs, which is a trademark of the Blu-ray Disc Association. The Blu-ray disc format typically contains 5-10 times as much stored information as the predecessor DVD optical data storage format, which was based on the capabilities of red laser diodes. In addition to their usefulness for optical data storage, GaN-based laser diodes could also be extremely useful for projection displays, among other applications.
Conventional GaN-based laser diodes were fabricated on c-plane sapphire substrates, utilizing epitaxial lateral overgrowth techniques to reduce the high concentration of threading dislocations which form at the sapphire/GaN interface. The c-plane substrate orientation was utilized mainly because smooth epitaxial layers could be obtained. Later, as high quality bulk GaN substrates began to become available, laser diode manufacturers began to switch from the use of sapphire as a substrate to bulk GaN. An example of a homoepitaxial laser diode is disclosed by U.S. Pat. No. 6,936,488, which is hereby incorporated by reference in its entirety. However, for the most part, most laser diode manufacturers continued to use the c-plane orientation.
Existing methods suffer from a number of limitations. First, the efficiency of light emission in the nitrides tends to fall off markedly as the emission wavelength is increased from violet to blue, green, and beyond. Practical c-plane GaN-based laser diodes have not yet been demonstrated in green or longer wavelengths. Bright green laser diodes are needed in order to enable projection applications, in combination with blue and red laser diodes. A second limitation is that the threshold current of the devices is sometimes undesirably high, which decreases the efficiency of the devices. A third limitation is that the yield of intact devices tends to be small, mainly due to breakage during the fabrication process.
From the above, it is seen that improved techniques for developing gallium containing substrates are highly desired.